Re: Can someone please explain the 23rd-and-24th-century starship clas
You also have to remember that the capabilities of all the ships in question were at the whim and mercy of the writers and directors of that week. Two cases in point - The Borg & The Dominion (specifically the Jem'Hadar). Both adversaries gave the Federation a blood-letting they will never forget at first meeting. While later on, both had ships that no longer seemed to pack the punch that they did in the beginning.
IIRC, Jem'Hadar shields couldn't be easily penetrated by phasers (I somehow remember this being the case at one point). They were throwing their bug ships at a Galaxy-class ship like they were totally disposable, wiping it out in minutes. Then, later on, during the various series-end battles of the Dominion War, they were being cut up by legacy Klingon Birds of Prey like butter. And what ever happened to the Vorta's curious mental telepathy force burst? It was only ever shown once by Eris (sp?) and never seen again by the army of Weyoun's. The shows are full of these inconsistencies and the ship capabilities are especially susceptible to continuity drift.
The "unstoppable force of nature" that Q introduced to the Federation in the form of the Borg was reduced to a gaggle of feckless Cylon/Stormtrooper wanna-be's by the time Voyager and Future-Janeway got through with them.
The reasoning is obvious and totally the fault of the story - ramp up the artificial tension and threat and overcome all odds without much explanation as to why our heroes succeeded other than the fact than they were our heroes. DS9 did a reasonably better job of it, I think, than Voyager did, but that's a topic for another thread.
You can probably find some semi-reliable information about these ships online (dimensions, mass, crew compositions, etc.), but comparing them at a tactical level, I'm thinking, would be folly due to their internal inconsistencies.
Another thing you need to remember - class designations like "Heavy Cruiser", "Frigate", etc., were never widely used in the canonical Trek universe, if really at all. In fact, I don't think the word "Frigate" ever entered a single line of dialog in any of the series and movies, yet it is an accepted class designation - to the fandom at-large - to describe ships of the Reliant's design (larger primary hull, no secondary hull, under-slung warp engines) - a design which some have also referred to as "Light Cruiser" as well. Naming classification types such as these were more an affectation by the fandom (likely starting with Franz Joseph) to categorize the growing stable of ship designs, consistent with current customs, usages and naming conventions of modern-day naval craft. Shit, we didn't get a class-name for the Reliant (Miranda) or Grissom (Oberth) until we were well within Next Generation's run due to the reuse of the studio models as guest ship appearances - and there are STILL ongoing and colorful discussions of whether the refit Enterprise is "Constitution Class", "Enterprise Class", "Constitution II Class" or simply "Starship Class". It's fun to speculate, but I wouldn't loose too much sleep over finding a solid answer.